The spinal column is a highly complex system of bones (i.e., vertebral bodies) and connective tissues that provides support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one atop the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces on the spinal column. A vertebral canal containing the spinal cord and nerves is located within the forward-facing surface of the vertebral bodies.
There are many types of spinal column disorders. Patients that suffer from such disorders typically experience extreme and debilitating pain, as well as diminished nerve function. Examples of such spinal column disorders include, but are not limited to, scoliosis (i.e., abnormal lateral curvature of the spine), kyphosis (i.e., abnormal forward curvature usually in the thoracic portion of the spine), excess lordosis (i.e., abnormal backward curvature usually in the lumbar portion of the spine), spondylolisthesis (forward displacement of one vertebrae over another usually in the lumbar portion or cervical portion of the spine), etc. There are still other types of spinal column disorders caused by physiological abnormalities, disease and/or trauma such as, for example, ruptured or slipped discs, degenerative disc disease, fractured vertebra, and the like.
Multi-segmental spinal fixation is an accepted surgical procedure in the treatment of such spinal column disorders. It involves the use of a series of pedicle screw assemblies and one or more spine rods. The pedicle screw assemblies each include a screw that is threadedly screwed into one of a plurality of adjacent vertebral bodies. A spine rod (contoured or straight) is fixedly secured to a spine rod clamping body of each one of the pedicle screws for fixing two or more adjacent vertebral bodies in a static relative position. In this manner, spinal fixation can be used to alter the alignment of adjacent vertebrae relative to one another so as to change the overall alignment of the spine, to preclude relative movement between adjacent vertebrae, and the like.
The effectiveness of multi-segmental spinal fixation is dependant on several considerations. Examples of such considerations include, but are not limited to, the ability of a pedicle screw assembly to readily and rigidly accommodate a spine rod bent to the contour of the spine, the ability of a pedicle screw assembly to reliably secure the bent spine rod in a fixed position and orientation, the ability of a screw of a pedicle screw assembly to be threadedly engaged with a vertebral body in a manner that provides acceptable mechanical strength, and the ability of a screw of a pedicle screw assembly to be threadedly engaged with a vertebral body in a manner that minimized adverse deformation and/or damage to the vertebral body. Known pedicle screw assemblies are deficient in one or more of these considerations, thus limiting their effectiveness.
Therefore, a pedicle screw apparatus, pedicle screw system and/or a lock screw for use therewith that overcomes deficiencies associated with known pedicle screw implements would be advantageous, desirable and useful.